The present invention relates to the medical arts. It finds particular application in cardiac assist technologies using rotodynamic blood pumps, also known as left ventricular assist devices (LVAD) in assisting patients with failing hearts and will be described with particular reference thereto. It is to be appreciated that the present invention is also applicable to other types of pumps, and is not limited to the aforementioned application.
Rotodynamic pumps (axial flow, mixed flow, and centrifugal) have prospective applications in cardiac assist technologies. A typical cardiac assist system includes the blood pump itself, electric motor (usually a brushless DC motor integrated into the pump), drive electronics, microprocessor control unit, and an energy source, such as rechargeable batteries. These pumps can be used in fully implantable systems for chronic cardiac support where the whole system is located inside the body and there are no drive lines penetrating the skin. For more temporary support, the pump is located inside the body but some system components, including drive electronics and energy source, may be placed outside the patient body.
The inverted, shaftless, brushless motor design is utilized because it has a significant advantage over typical motor/drive shaft configurations. There are no openings in the housing that would allow blood into the motor, and the housing precludes air or other fluid from entering the bloodstream. A primary drive impeller of the pump encloses a drive magnet and is driven by a stator and coil assembly disposed radially inward from the motor rotor, i.e., an inverted motor. In order to avoid friction and subsequent heat buildup, the blood of the patient is used as a fluid bearing between the impeller and the stator.
A potential problem with this system is that the blood can become heated and/or stagnant, and partially solidify by forming a thrombus or heat coagulation of blood proteins on the stator housing surface or on the secondary impeller of the motor rotor in the inverted fluid film bearing assembly. Such a situation is undesirable and potentially life-threatening to the patient who is dependant on the proper function of such a device. Accordingly a need exists for a well-washed or continuous flow of blood that serves as the bearing between the rotor and stator components.
The present invention provides a new and improved method and apparatus that avoids thrombus and/or coagulated protein formation/deposition and overcomes the above referenced problems and others.